#include <bits/stdc++.h>
using namespace std;
#define ll long long
vector<vector<vector<ll>>> v;
vector<priority_queue<ll>> pr;
ll ans = 0, n, fi;
void dfs(int x, ll co){
if (v[x].size() == 0){
pr[x].push(co);
pr[x].push(co);
ans -= co;
return;
}
int cnt = 0;
for (auto el : v[x]){
cnt++;
dfs(el[0], el[1]);
if (pr[el[0]].size() > pr[x].size()){
swap(pr[el[0]], pr[x]);
}
while (!pr[el[0]].empty()){
pr[x].push(pr[el[0]].top());
pr[el[0]].pop();
}
}
int wh = 0;
if (x != 1) wh++;
for (int i = wh; i < cnt; i++){
ans += pr[x].top();
pr[x].pop();
}
if (x != 1){
ll fi = pr[x].top();
pr[x].pop();
ll se = pr[x].top();
pr[x].pop();
pr[x].push(fi + co);
pr[x].push(se + co);
ans -= co;
}
}
int main(){
ll a, b;
cin>>fi>>n;
n += fi;
v.assign(n + 1, vector<vector<ll>>());
pr.assign(n + 1, priority_queue<ll>());
for (int i = 2; i <= n; i++){
cin>>a>>b;
v[a].push_back({i, b});
}
dfs(1, 0);
cout<<ans;
}
